Saturday, April 27, 2013

“Neil Shubin is the kind of guy you’d like to meet at a cocktail party: smart, funny, a good storyteller . . . It’s unfortunate that Dr. Shubin . . . has ignored the starkly challenging era we live in.”

Paleontologist Neil Shubin is the kind of guy you’d like to meet at a cocktail party: smart, funny, a good storyteller who can drop your jaw with scientific insights on how that jaw developed thanks to obscure creatures from other eons.

Author of the bestselling Your Inner Fish, Dr. Shubin doesn’t merely explain science with clarity and humor; he unearths some of those connections in his own fieldwork.

In The Universe Within: Discovering the Common History of Rocks, Planets, and People Dr. Shubin relates how cosmic and chemical forces of the universe's 13.7 billion-year evolution shaped our bodies and the Earth we inhabit.

Although probably the best fit for readers with a basic interest in science, Dr. Shubin’s book includes both landmark and late-breaking research. Written during simpler times, it would have been enjoyably informative; however, the gap between what the author does with his extensive knowledge, and what he could have done to serve his readers, is extremely frustrating. More about that later.

The Universe Within is as much about the people who moved science forward in discovering evolution's cosmic links as it is about their ideas.

Not all of them were professional scientists: There were bored civil servants, a tea shop owner, and many women—the earliest of whom were denied a scientific education. For example, astronomy research accelerated thanks to the late 19th century’s “Harvard Computers”—women (including the housekeeper of the Harvard College Observatory’s director)—who caught pivotal astronomical changes while laboriously cataloguing photographic plates of stars and nebulae in that pre-computer age.

Also compelling is Dr. Shubin’s detailed yet conversational style as he unrolls the story of the Big Bang and its evolutionary course. While it’s familiar territory to many, modern humans need to hear this story until our intimate connections with other species sink in.

Unfortunately, throughout his book, Dr. Shubin misses opportunities to make those connections.

Literally, the book delivers what it promises—a common history—but is this enough when the species reading this book is threatening any common future? For example, Dr. Shubin cursorily mentions previous major extinctions that have rocked the Earth’s life systems in the wake of asteroids, climate change, and plate tectonics. “There are five intervals where the numbers of species just crash,” he says.

But he neglects to mention that Earth is now suffering the sixth major extinction, the only one caused by a species (guess who?), in which other species are being snuffed out at 1,000 times the usual rate.

Dr. Shubin devotes about 50 pages to catastrophe theory and to the mechanics of Earth’s earlier climate fluctuations. He describes possible causes for these shifts: tilts in planetary orbit, ocean current changes, or the rising of the Tibetan Plateau and subsequent increased rock weathering. Toward the section’s conclusion, he notes:

“The emerging picture is that Earth’s climate depends on the heat balance on the planet—the amount of heat coming in from the sun minus the heat escaping into space—and the ways that this heat is transferred among the oceans, land, air, and ice.”

Wouldn’t this be the author’s cue to discuss the human disruption of that balance? Unfortunately, it goes unmentioned—even though the equivalent of 400,000 Hiroshima bomb explosions add more heat to that imbalance every day.

Dr. Shubin’s “amount of heat coming in from the sun” doesn’t explain the whole picture, since this gain has occurred during an extreme solar minimum. That same information has driven NASA climate scientist James Hansen (whose figures these are) to protest and get arrested in front of the White House. Instead, Dr. Shubin follows with: “Music is an analogy for what drives climate . . .” with its “long-term rhythm and short-term riffs.”

That discussion ends with his introduction to how some humans survived the abrupt climatic shift 12,500 years ago, sounding more like the CEO of Exxon Mobil responding to climate critics with “we’ll adapt” than a leading scientist. The author ignores Earth's current challenges often enough to be utterly maddening.

What accounts for this blind eye? Although slim, The Universe Within includes detailed descriptions of colleagues’ messy offices, academic politics, and the small towns where big scientists grew up. Is Dr. Shubin reluctant to step from the data to the larger picture—to meaning?

Scientists have traditionally shied from making meaning out of their work, likely a remnant from historic efforts to emancipate science from Church interference. However, that barricade has long been breached, by no less than Albert Einstein, Carl Sagan, biologists E.O. Wilson and Richard Dawkins, mathematical cosmologist Brian Swimme, and fellow paleontologist Pierre Teilhard de Chardin.

The Universe Within concludes with an upbeat “With virtually every technology and idea, our species has found new ways to insulate ourselves from the planet . . . it has been eleven thousand years since the dawn of our civilization. With the ever-increasing pace of change around us, imagine what humans will be capable of in another eleven thousand.”

Really?

Recent newspaper headlines show how well people in the Great Plains and the East Coast of the U.S. have been able to insulate themselves from the planet—if in fact that’s a desirable response.

Dr. Shubin’s avatar for the techno-fix is equally problematic: plant biologist Norman Borlaug, who won the Nobel Prize for his role in the late 20th century Green Revolution, which Dr. Shubin credits as “bettering or saving the lives of millions of people around the world.”

What he doesn’t mention is the dark side of Borlaug’s legacy: aquifers depleted by the irrigation demands of his hybrid grains; negative health and environmental impacts of the Green Revolution's chemical fertilizers and pesticides; and the crippling dependency of third world farmers on Monsanto, Cargill, and other industrial agriculture giants for seeds, chemical inputs, and crop prices.

The Universe Within contains many valuable facts, histories, and theories; however, it reads as if it were written in a vacuum.

It’s unfortunate that Dr. Shubin, with his great knowledge of geologic time and his skills in relating evolutionary events to a general audience, has ignored the starkly challenging era we live in.

Reviewer

Maria Theresa Stadtmueller received an MFA from The University of Iowa Nonfiction Writing Program. She also participated in the Bread Loaf Writers’ Conference. She’s been a stand-up comic in New York, an environmental marketing writer in Seattle, and a chamber music impresaria in San Francisco.

"Tiktaalik lived approximately 375 million years ago. Paleontologists suggest that it is representative of the transition between non-tetrapod vertebrates (fish) such as Panderichthys, known from fossils 380 million years old, and early tetrapods such as Acanthostega and Ichthyostega, known from fossils about 365 million years old. Its mixture of primitive fish and derived tetrapod characteristics led one of its discoverers, Neil Shubin, to characterize Tiktaalik as a "fishapod".[3][4]"

"Tiktaalik (pron.: /tɪkˈtɑːlɨk/) is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the late Devonian period, with many features akin to those of tetrapods (four-legged animals).[1] It is an example from several lines of ancient sarcopterygian fish developing adaptations to the oxygen-poor shallow-water habitats of its time, which led to the evolution of tetrapods.[2] Well-preserved fossils were found in 2004 on Ellesmere Island in Nunavut, Canada."

"Two primitive meteorites collected in Antarctica appear to contain grains of silica—the stuff of quartz and sand—forged in an ancient supernova that predates the birth of the solar system. In fact, some researchers believe that it was just such a stellar explosion that triggered the formation of the solar system from a cloud of dust and gas billions of years ago. Whether or not the Antarctic meteorites contain a record of that fateful cataclysm, they do contain a supernova by-product that has never before been found on Earth."

"You never hear of the other Lyell. Sir Charles, you know quite well: he set the infant science of geology firmly on its feet and inspired Charles Darwin. But there’s another Lyell who was a geologist, and without her, Charles Lyell would have found his work far more difficult, if not impossible. When he married Mary Horner, he pledged himself to a lifelong scientific partner."

"The astronomy, calendar, and apocalyptic predictions have been well documented, but there's one part of Maya history that researchers have yet to agree upon: how the ancient civilization actually came to be."

"Fractals aren't just something you learn about in math class. They are also a gorgeous part of the natural world. Here are some of the most stunning examples of these repeating patterns that look the same no matter how far you zoom in or out."

"CHICAGO — The nation’s midsection, which was for months parched by severe drought, suddenly finds itself contending with the opposite: severe flooding that has forced evacuations, slowed commercial barge traffic down the Mississippi River and left farmers with submerged fields during a crucial planting time."

what is a white dwarf?- a white dwarf is the most inert core of a dead star-electron degeneracy pressures balances the inward pull of gravity

what can happen to a white dwarf in a close binary system?-matter form its close binary companion cab fall onto the white dwarf through an accretion disk-accretion of matter can lead to novae and white dwarf novae

what is a neutron star?-a ball of neutrons left over form a massive star supernova and supported by neutron degeneracy pressure

How were neutron stars discovered?-beams of radiation form a rotating neutron star sweep through space like lighthouse beams, making the appear to pulse-observations of these pulses wee the first evidence for neutron stars

what can happen to a neutron star in a close binary system?-the accretion disk around a neutron star gets hot enough to produce X-rays,making the system an X-ray binary-sudden fusion events periodically occur on the surface of an accreting neutron star,producing X-rays bursts

what is a black hole?-a black hole is a massive object whose radius is so small that the escape velocity exceeds the sped of the light

What would it be like to visit a black hole?-you can orbit a black hole like any other object of the same mass-black holes don't suck-near the event horizon,time slows down and tidal forces are very strong

1. What is a white dwarf?A white dwarf is the most inert core of a dead star. The electron degeneracy pressures balances the inward pull of gravity.

2. What can happen to a white dwarf in a close binary systemA white dwarf in a close binary system can acquire hydrogen from its companion through an accretion disk. The hydrogen builds up on the white dwarf’s surface, it produces with nuclear fusion to make a nova.

3. What is a neutron star?A ball of neutrons left over form a massive star supernova and supported by neutron degeneracy pressure

4. How were neutron stars discovered?By beams of radiation form a rotating neutron star sweep through space like lighthouse beams, making the appear to pulse. Also observations of these pulses wee the first evidence for neutron stars.

5. What can happen to a neutron star in a close binary system?The accretion disk around a neutron star gets hot enough to produce X-rays,making the system an X-ray binary. The sudden fusion events periodically occur on the surface of an accreting neutron star,producing X-rays bursts.

6. What is a black hole?A black hole is a massive object whose radius is so small that the escape velocity exceeds the sped of the light.

7. What would it be like to visit a black hole?You can orbit a black hole like any other object of the same mass-black holes don't suck. Near the event horizon,time slows down and tidal forces are very strong.

9. What causes gamma ray bursts?Gamma-ray bursts occur in distant galaxies and are the most powerful bursts of energy that are anywhere in the universe. The precise cause is unknown, yet at least some appear to come from unusually powerful supernovae.

10. What did Jocelyn Bell discover? Jocelyn Bell discovered the first neutron star by using a radio telescope. Jocelyn also notices a very regular pulses of radio emission coming from a single part of the sky.

Thursday, April 25, 2013

A white dwarf is the left over core from a dead low-mass star. White dwarfs are supported by electron degeneracy pressure against the crush of gravity. They typically have the same mass as the Sun, but are no larger than Earth. No white dwarf can have a mass greater than 1.4 MSun and higher mass white dwarfs are typically smaller in size.

What can happen to a white dwarf in a close binary system?

A white dwarf in a close binary system can acquire hydrogen from its companion through an accretion disk. A star that started with less mass gains mass from its companion. As hydrogen builds up on the white dwarf's surface, it may begin nuclear fusion and cause a nova. In some extreme cases, accretion may continue until the white dwarf's mass exceeds the white dwarf limit, causing it to explode as a white dwarf supernova.

What is a neutron star?

A neutron star is a ball of neutrons created by the collapse of the iron core in a massive supernova.

How were neutron stars discovered?

Neutron stars were discovered through pulsars, which were the first evidence of neutron stars. Neutron stars spin rapidly when they are born. Their strong magnetic fields can direct beams of radiation through space. while the neutron star rotates. We see these neutrons stars as pulsars.

What can happen to a neutron star in a close binary system?

Neutron stars in a close binary system can accrete hydrogen from their companions, forming accretion disks. Accreting matter adds angular momentum to the neutron star, increasing its spinning. This matter can eventually become hot enough for helium to fuse, causing x-ray bursts.

What is a black hole?

A black whole is an object whose gravity is so powerful that not even light can escape it. The spherical surface, the event horizon, of the black whole is the radius at which the escape velocity is the speed of light. Nothing can escape a black whole because nothing can move faster than the speed of light.

What would it be like to visit a black hole?

You could orbit a black hole because there is no sucking action. Time would seem to run slowly for objects falling toward the black hole. Light would be red-shifted as the object approached the hole.

Do black holes really exist?

Some x-ray binaries include compact objects that are far too massive, mass exceeding 3 MSun, to be neutron stars, making it likely that they are black holes.

What causes gamma ray bursts?

The cause of gamma ray bursts is not exactly known, but the energy required to make a burst suggests that some gamma ray bursts appear to come from powerful supernova explosions that create black holes. Other gamma ray bursts may come from mergers of neutron stars in close binary systems, causing black holes.

What did Jocelyn Bell discover?

In 1967, Jocelyn Bell discovered a regular pulse (pulsars) of neutron stars using a radio telescope.

What is a white dwarf? A white dwarf is the core left over from a low mass star, supported against the crush of gravity by electron degeneracy pressure. A white dwarf typically has the mass of the Sun compressed into a size no larger than Earth. No white dwarf can have a mass greater than 1.4M Sun.

What can happen to a white dwarf in a close binary system? A white dwarf in a close binary system can acquire hydrogen from its companion through an accretion disk that swirls toward the white dwarf's surface. As hydrogen builds up on the white dwarf's surface, it may begin nuclear fusion and cause a nova that, for a few weeks, may shine as rightly as 100,000 Suns.

What is a neutron star?A neutron star is the ball of neutrons created by the collapse of the iron core in a massive star supernova. It resembles a giant atomic nucleus 10 km in radius and with more mass than the Sun.

How were neutron stars discovered? Neutron stars spin rapidly when they are born, and their strong magnetic fields can direct beams of radiation that sweep through space as the neutron star spins,. We see such neutron stars as pulsars, and these pulsars provided the first direct evidence for the existence f neutron stars.

What can happen to a neutron star in a close binary system? Neutron stars in close binary systems can accrete hydrogen from their companions, forming dense, hot accretion disks. The hot gas emits strongly in X rays, so we see these systems as X-ray binaries. In some of these systems, frequent bursts of helium fusion occur on the neutron star's surface, causing X-ray bursts.

What is a black hole? A black hold is a place where gravity has crushed matter into oblivion, creating a hole in the universe from which nothing can ever escape, not even light. The event horizon marks the boundary between our observable universe and the inside of the black hold; the black hole's Schwarzschild radius is the size of the event horizon.

What would it be like to visit a black hole? You could orbit a black hole just like you could any other object of the same mass. However, you's see strange effects for an object falling toward the black hole: Time would seem to run slowly for the object, and its light would be increasingly red-shifted as it approached the black hole. The object would never quite reach the event horizon, but it would soon disappear from view as its light became so redshifted that no instrument could detect it.

Do black holes really exist? No known force can stop the collapse of a stellar corpse with a mass above the neutron star limit of 2 to 3 solar masses, and theoretical studies of supernovae suggest that such objects should sometimes form. Observational evidence supports this idea: Some X-ray binaries include compact objects far too massive to be neutron stars, making it likely that they are black holes.

What causes gamma ray bursts? No one knows exactly how gamma ray bursts are produced, but the energy required to make one suggests that gamma ray bursts occur when certain kinds of black holes are formed. At least some gamma ray bursts appear to come from unusually powerful supernova explosions that may create black holes. Others may come from the creation of black holes through mergers of neutron stars in close binary systems.

What did Jocelyn Bell discover? She discovered the first radio pulsars with her thesis supervisor Antony Hewish.

White dwarfs are the remaining cores of dead stars. Electron degeneracy pressure supports them against gravity. White dwarfs cool off and grow dimmer with time. White dwarfs with the same mass as the sun are the same size of Earth. Higher mass white dwarfs are smaller. Quantum mechanics says that electrons must move faster as they are squeezed into a very small space. As a white dwarfs mass approaches 1.4m its electrons must move at nearly the speed of light. Because nothing can move faster than light a white dwarf cannot be more massive than 1.4.

What can happen to a white dwarf in a close binary system?

A star started with less mass gains mass from its companion. Mass falling toward a white dwarf from its close because. has Some angular motion. The matter therefore orbits the white dwarf in an acceleration disk.

What is a neutron star?

A neutron star is the ball of neutrons left behind by a massive star supernova.

How were neutron stars discovered?

Using a radon telescope in 1967 Jocelyn Bell noticed a regular pulse.

What can happen to a neutron star in a close binary system?

Matter falling toward a neutron star forms an acceleration disk.

What is a black hole?

A black hole is an object that’s so powerful that not even light can escape.

What would it be like to visit a black hole?

Time passes more slowly near the event horizon

Do black holes really exist?

Needs to measure mass. use orbital properties of companion measure velocity and distance of orbiting gas.

What causes gamma ray bursts?

Brief bursts of gamma rays coming from space were first detects in the 1960s.

13.1What is a white dwarf?-White dwarfs are the remaining cores of dead stars.-Electron degeneracy pressure supports them against gravity.-White dwarfs cool off and grow dimmer with time.-White dwarfs with the same mass as the sun are the same size of Earth.-Higher mass white dwarfs are smaller.-Quantum mechanics says that electrons must move faster as they are squeezed into a very small space.-As a white dwarfs mass approaches 1.4m its electrons must move at nearly the speed of light.-Because nothing can move faster than light a white dwarf cannot be more massive than 1.4.

What can happen to a white dwarf in a close binary system?-A star started with less mass gains mass from its companion.-Mass falling toward a white dwarf from its close because. has Some angular motion.-The matter therefore orbits the white dwarf in an acceleration disk.-The temperature of accreted matter eventually becomes hot enough for hydrogen fusion.-Fusion begins suddenly and explosively causing a nova.-The nova star system temporarily appears Much brighter.-The explosion drives accreted matter out into space.-Massive star supernovas have iron cores of massive star reaches. white dwarf limit and collapses into a neutron star causing an explosion.-White dwarf supernova is carbon fused suddenly begins as a white dwarf in close binary system reaches white dwarf limit causing Total explosion.-One way to tell supernova types apart is with a light curve showing How luminosity changes with time.-Supernova are Much Much more luminous Than novae.-Nova is H to He fusion of layer of accretes matter white dwarf left intact.-Supernova a complete explosion if white dwarfs.-Light curves differ-Spectra differ exploding white dwarfs don't have hydrogen absorption lines.

13.2What is a neutron star?-A neutron star is the ball of neutrons left behind by a massive star supernova.-The degeneracy pressure of neutrons supports a neutron star against gravity.-Electron degeneracy pressure goes away because electrons combines with protons making neutrons and neutrinos.-Neutrons collapse to the center forming a neutron star.-A neutron star is the same size as a small city.

How were neutron stars discovered?-Using a radon telescope in 1967 Jocelyn Bell noticed a regular pulse.-Pulsar at center of Crab nebula pluses 30 times per second.-A pulsar is a neutron star that beams radiation along a magnetic axis that is not aligned with the rotation axis.-The radiation beam sweep through space like a light house beams as the neutron star rotates.

What can happen to a neutron star in a close binary system? - Matter falling toward a neutron star forms an acceleration disk.-Accreting matter adds angular momentum to a neutron star increasing spinning.-Matter accreting onto neutron star can eventually become hot enough for helium to fuse.-Quantum mechanics says that neutrons in the same place cannot be in the same state.-Neutron degeneracy pressure can no longer support a neutron star against gravity if its mass exceeds about 3M.

13.3What is a black hole?-A black hole is an object that’s so powerful that nit even light can escape.-light would not be able to Escape earths surface if you could shrink it.-The surface of a black hole is the radius at which the escape of velocity equals the speed of light.-The spherical surface is known as the event horizon.-The radius of the event horizon is known as Schwarzschild radius -the event horizon of 3m black hole is also about as bug as a small city.-A black holes mass strongly wraps space and time in vicinity of the event horizon.-Nothing can Escape from within the event horizon because nothing can to faster than light.-No Escape means there is no contact with something that falls in. it increases the holes mass changes its spin or charge but otherwise loses its identity.-Beyond the neutron star limit no known force can resist the crush of gravity.-As far as we know gravity crushes all the matter into a single point known as a singularity.

What would it be like to visit a black hole?-If the sun shrank into a black hole its gravity would be different only near the event horizon.-Light waves take extra time to climb put of a deep hole I'm space-time leading to gravitational red shift.-Time passes more slowly near the event horizon.-Tidal force near the event horizon of a 3M black hole would be lethal to humans.-Tidal forces would be gentler near a super massive black hole because its radius is much bigger.

Do black holes really exist?-Needs to measure mass. use orbital properties of companion measure velocity and distance of orbiting gas.-If its a black hole if its not a star its mass exceeds the neutron star limit .-Some x ray binaries contain compact objects of mass exceeding 3m.-One famous x-ray binary with a black hole is in a constellation.

13.4What causes gamma rays to burst.-Brief bursts of gamma rays coming from space were first detects in the 1960s.-Observations in the 1990s showed that gamma rays bursts were coming from very distant galaxies.-They must be among the most powerful explosions.-Observations show that at least Some gamma rays bursts are produced by supernova explosions.

A white dwarf is the core left over from a
low-mass star, supported against the crush of gravity by electron degeneracy
pressure.

2.What can happen to a white dwarf in a close
binary system

A white dwarf in a close binary system can
acquire hydrogen from its companion through an accretion disk. As hydrogen
builds up on the white dwarf’s surface, it may ignite with nuclear fusion to make
a nova.

3.What is a neutron star?

A neutron star is the ball of neutrons created
by the collapse of the iron core in a massive star supernova.

4.How were neutron stars discovered?

Neutron stars spin rapidly when they are
born, and their strong magnetic fields can direct beams of radiation that sweep
through space as the neutron star spins. We see such neutron stars as pulsars,
and these pulsars provided the first direct evidence for the existence of
neutron stars.

5.What can happen to a neutron star in a close
binary system?

Neutron stars in close binary systems can
accrete hydrogen from their companions, forming dense, hot accretion disks. The
hot gas emits strongly in X rays, so we see these systems as X-ray binaries. In
some of these systems, frequent bursts of helium fusion ignite on the neutron
star’s surface, emitting X-ray bursts.

6.What is a black hole?

A black hole is a place where gravity has
crushed matter into oblivion, creating a true hole in the universe from which
nothing can ever escape, not even light.

7.What would it be like to visit a black hole?

Time would seem to run slowly for the object.
Its light would be increasingly redshifted as it approached the black hole. The
object would never quite reach the event horizon, but it would soon disappear
from view as its light became so redshifted that no instrument could detect it.

8.Do black holes really exist?

No known force can stop the collapse of a
stellar corpse with a mass above the neutron star limit of 2 to 3 solar masses,
and theoretical studies of supernovae suggest that such objects should
sometimes form. Observational evidence supports this idea.

9.What causes gamma ray bursts?

Gamma-ray bursts occur in distant galaxies and
are the most powerful bursts of energy we observe anywhere in the universe. No one
knows their precise cause, although at least some appear to come from unusually
powerful supernovae.

10.What
did Jocelyn Bell discover?

She discovered the first neutron star by
using a radio telescope. She notices a very regular pulses of radio emission
coming from a single part of the sky.

"YUXI, China — Many residents of this tiny village in the mountainous region of southwest China spent Saturday night in tents and makeshift shelters, too scared to sleep in their flimsy homes after an earthquake killed 160 people early that morning."

How do stars form?Stars form in dark clouds of dusty gas in interstellar space. The gas between the stars called the interstellar medium. Gravity can create stars only if it can overcome the force of thermal pressure in a cloud. Also, gravity within contracting gas cloud becomes stronger as the gas becomes denser.

How massive are newborn stars?A cluster of many stars can form out of a single cloud. They very massive stars and are rare. Also, low mass stars are common.

What are the life stages of a low-mass star?A star remains in the main sequence as long as it can fuse hydrogen into helium in its core. The Life track after main sequence is observations of stars cluster show that a star become larger redder and more luminous after its time on the main sequence is over.

How does a low-mass star die?Double shell fusion, which is; after core helium fusion stops, He fuses into carbon in a shell around the carbon core, and H fuses to He in a shell around the helium layer. This double shell fusion stage never reaches equilibrium the fusion trade periodically spikes.

What are the life stages of a high-mass star?A high mass star lives a much shorter life than a low mass star, fusing hydrogen into helium via the CNO cycle. After exhausting its core hydrogen , high mass star begins hydrogen shell fusion and then goes through a series fusing successively heavier elements. The furious rate of this fusion makes the star swell in size to become supergiant.

How do high-mass stars make the elements necessary for life?

in its final stages of life, a high mass stars core becomes hot enough to fuse carbon and other heavy elements. the variety if different fusion reactions produces a wide range of elements-including all the elements necessary for life- that are then released into space when that stars dies.

How does a high-mass star die?A high mass star dies in a cataclysmic explosion called supernova, scattering newly produced elements into space and leaving behind a neutron star or black hole. The supernova occurs after fusion begins to pile up iron in the high mass star's core.Because iron fusion cannot release energy, the core cannot hold off the crush of gravity for long. In the instant that gravity overcomes degeneracy pressure, the core collapses and the star explodes.

How does a star's mass determine the life story?

A star's mass determines how it lives its life. Low-mass stars never get hot enough to fuse carbon or heavier elements in their cores and end their lives by expelling their outer layers and leaving white dwarfs behind. High-mass stars live short but brilliant lives, ultimately dying in supernova explosions.

How are the lives of stars with close companions different?When one star in a close binary system begins to swell in size at the end of its main-sequence stage, it can begin to transfer mass to its companion. This mass exchange can then change the remaining life histories of both stars.

12.1How do star form?-stars form in dark clouds of dusty gas in interstellar space-e gas between the stars called e interstellar medium - gravity can create stars only if it can overcome the force of thermal pressure in a cloud-gravity within contracting gas cloud becomes stronger as the gas becomes denserMass of a star forming cloud :--a typical molecular cloud must contain at least a few hundred solar masses of gravity to overcome ( T~30k, n~300 particles/ cm^3)- the cloud can prevent a pressure build up by converting thermal energy into infrared and radio photons that escape the cloud fragmentation of cloud:-ThIs simulation begins with a turbulent cloud counting 50 solar masses of gas-the random moons of different sections of the cloud cause it to become lumpy -Each lump of the cloud in which gravity can overcome pressure can go on to become a star-a large cloud can make a whole cluster of stars

Glowing dust grains:-as star begin to form , dust grains that absorb visible light heat up and emit infrared light -long wavelength infrared light is brightest from regions where many stars are currently forming

-Solar system formation is a good example of star birth-Cloud heats up as gravity causes it to contract due to conservation of energy. Contraction can continue if thermal energy radiated away. - as gravity forces a cloud to become smaller , it begins to spin faster and faster due to conservation of angular momentum. -as gravity forces a cloud to become smaller it begins to spin faster and faster due to conservation of angular momentum . Gas settles into spinning disk because spin hampers-flattening : collision between particles in it cause it to flatten .Formation of jets : -rotation also causes jets of matter to shoot out Along the rotation axis-jets are observed coming from the centers of disks around protostars Protostar to main sequence:-Protostar contracts and heats until the core temp is sufficient for hydrogen fusion-contraction ends when energy released by hydrogen fusion balances energy radiated form the surface-it takes 30 million years for a star like the Sun( less time for more massive stars)

-a cluster of many stars can form out of a single cloud -very massive stars are rare-low mass stars are common

Upper limits in a stats mass:-photons exert a slight amount of pressure when they strike matter-very massive stars are so luminous that the collective pressure of photons drives their matter into space -models of stars suggest that radiation pressure limits how massive a star can be without blowing itself apart-observations have not found stars more massive than about 300MsunLower limits : -fusion will not begin in contracting cloud if some sort of force stops contraction before the core temp rises above 10^7 K-thermal pressure cannot stop contraction because the star is constantly losing thermal energy from its surface through radiation

Degeneracy pressure :-Laws if quantum mechanics prohibit two electrons from occupying the same state in the same place

Thermal pressure: depends on heat content -the main form of pressure in most stars

Degeneracy pressure:-particles can't be in same state in same place-doesn't depend on heat content

Brown dwarfs :- degeneracy pressure halts the contraction of objects with <.08Msun before the core temp becomes hot enough for fusion-starlike objects not massive enough to start fusion are brown dwarfs- a brown dwarf emits infrared light because of heat leftover from contraction

Brown dwarfs in Orion:-infrared observations can reveal recently formed brown dwarfs because that are still relatively warm and luminous

12.2 Life as Low Mass stars :

What are the life stages of a low mass star?-a star remains in the main sequence as long as it can fuse hydrogen into helium in its core

Life track after main sequence :-observations of stars cluster show that a star becomes larger redder and more luminous after its time on the main sequence is over

Broken thermostat :-as the core contracts H begins fusing to He in a shell around the core-luminosity increases because the core thermostat is broken, the increasing fusion rate in the shell does not stop the core from contracting

-helium fusion does not begin right away because it requires higher temp than Hydrogen fusion larger charge leads to greater repulsion-The fusion of two helium nuclei doesn't work so helium fusion must combine three He nuclei to make carbonHelium flash -thermostat is Bren in low mass red giant because degeneracy pressure supports the core

-Helium core fusion stars enthused shrink nor grow because the core thermostat is temp fixed-models show that red giant should shrink and become less luminous after helium fusion begins in the core-Combining models of stars of similar age but different mass helps us to age date star clusters how does a low mass star die?Double shell fusion :-after core helium fusion stops, He fuses into carbon in a shell around the carbon core, and H fuses to He in a shell around the helium layer-this double shell fusion stage never reaches equilibrium the fusion trade periodically spikes

-Double shell fusion ends with a pulse that enacts the H and He into space as a planetary nebula -the core left behind becomes a white dwarf

End of fusion :-fusion progresses no further in low mass star because the core temp never grows hot enough for fusion of heavier elements ( some He fuses to C to make oxygen)-degeneracy pressure supports the white dwarf-Life stages of low Mass star such as Sun

12.3 Life as a high mass star:

What are the life stages of high mass star?A high mass star lives a much shorter life than a low mass star, fusing hydrogen into helium via the CNO cycle. After exhausting its core hydrogen , high mass star begins hydrogen shell fusion and then goes through a series fusing successively heavier elements. The furious rate of this fusion makes the star swell in size to become supergiant.

How do high mass stars make the elements necessary for life?

in its final stages of life, a high mass stars core becomes hot enough to fuse carbon and other heavy elements. the variety if different fusion reactions produces a wide range of elements-including all the elements necessary for life- that are then released into space when that stars dies

How dies a high mass star die?

A high mass star dies in a cataclysmic explosion called supernova, scattering newly produced elements into space and leaving behind a neutron star or black hole. The supernova occurs after fusion begins to pile up iron in the high mass star's core.Because iron fusion cannot release energy, the core cannot hold off the crush of gravity for long. In the instant that gravity overcomes degeneracy pressure, the core collapses and the star explodes.

How does a star's mass determine the life story?

A star's mass determines how it lives its life. Low-mass stars never get hot enough to fuse carbon or heavier elements in their cores and end their lives by expelling their outer layers and leaving white dwarfs behind. High-mass stars live short but brilliant lives, ultimately dying in supernova explosions.

How are the lives of stars with close companions different?When one star in a close binary system begins to swell in size at the end of its main-sequence stage, it can begin to transfer mass to its companion. This mass exchange can then change the remaining life histories of both stars.